Field of Invention
The present invention relates to technologies in operation and control of electric power system, and more particularly to method and system for eliminating low-frequency oscillation between generators.
Description of Related Arts
At present, after an electric power system is subjected to a disturbance, insufficient damping or negative damping may lead to oscillation of approximately equal amplitude or increased amplitude to occur in the rotor angle, the rotating speed of the power generator and the related electrical quantities (such as the power flow on transmission lines, the bus voltages, etc.). Since the frequency is generally about 0.1-2.5 Hz, this oscillation is referred to as low-frequency oscillation in power system. Low-frequency oscillation can be divided into two types, which are local mode and inter-area mode. Generally speaking, the more is the number of units, the greater is the area, then the lower is the oscillation frequency.
After the power grids are interconnected in a large scale, low frequency oscillation may lead to dramatic fluctuation of power on transmission lines, which is a very important problem to be solved in power transmission control. Although PSS (Power System Stabilizer) can effectively damp the local low frequency oscillation, it cannot effectively damp the inter-area oscillation because only local information is used. As a result, a number of wide area damping controls in which the wide area information is integrated to the PSS are proposed. However, the questions as to how to select the measuring/feedback signal, and how to prevent delay in signal transmission which will lead to worsening control effect remain to be resolved.